The present invention relates to a printing head for use in dot printers and, more particularly, to a printing wire for said printing heads.
Typically, a conventional dot printer, which is known as a sort of impact printers, comprises a plurality of printing wires disposed in alignment with each other and corresponding in number to picture elements or elemental areas forming a character pattern, and is so constructed as to perform printing of desired characters by selectively energizing such wires while the printing head is driven to move at a constant speed. Since the printing head of this kind is frequently and repetitively operated, preferably, the printing head can well withstand to break and wear. To this end, as disclosed in U.S. Pat. No. 3,828,908, Japanese Patent Publication No. 57-1428, Japanese Utility Model Publication No. 57-45170, and Japanese Provisional Patent Publication Nos. 59-111862 and 59-111863, conventional printing heads generally consist of a main body member and a chip member secured to an outer tip end of the main body member, which is composed of a high fracture or break resistant wire such as a tungsten wire, a piano wire, a maraging steel wire, etc., whereas the chip member is made of a tungsten carbide alloy having high wear resistance. In these wire constructions, since the tungsten carbide alloy constituting the chip member becomes fragile at the melting point of the high fracture resistant wire forming the main body member, these members cannot be joined by means of welding. Therefore, to positively join the main body member and the chip member of the printing wire together, with an increased joining strength at their junction, in most cases, these members are secured with each other by means of brazing. However, in the case of utilizing such brazing process for the formation of the printing wire, since the whole of the wire is subjected to heating during brazing, the main body member and the chip member change in their properties and are thus deteriorated in durability and linearity, resulting in poor assembly accuracy and poor printing quality of the wire. Moreover, after completion of brazing, it is required to scrape a solder which protrudes outside the peripheral surface of the wire to enable the resulting printing wire to fit well to an associated wire guide member of the printing head which slidably receives the wire. The necessity of scraping makes it difficult to improve the productivity of the printing wire.